In offshore drilling environments it is necessary to supply hydraulic signals and fluids to the wellhead and the standard practice is to use a hydraulic sub-sea control umbilical hose for the purpose of the workover control where workover operations are performed on a sub-sea wellhead using a workover riser and/or for blow out preventer control and actuation. The standard practice has been to use a standard thermoplastic hydraulic subsea control umbilical hose, which umbilical hose contains a number of hoses for carrying fluid and may also carry electrical cabling and fibre optic cabling as required. Typically hoses and cables carried within an umbilical are of a multilayer reinforced structure such as are known in the art so that they have appropriate pressure containment, burst and compression resistance for the usage envisaged. An example of an umbilical of the type supplied by the applicant is shown in FIG. 1 in cross-section.
Normally these umbilicals are stored, deployed and recovered from hydraulic or air powered reels on the top side (for example on a ship or other offshore structure). Such umbilicals are deployed, operated and recovered through a route containing one, two or three sheaves (wheels or rollers) depending on the applications and heave compensation systems used. The umbilicals are subject to various tensile and bending loads during deployment, operation and recovery whilst paid off and paid onto a reel, over various sheaves, roller guides and heave compensation systems. In operation the umbilicals also experience fatigue motions (small movements to and fro) which are generally of a smaller displacement but with a higher cycle.
Typically an umbilical when operating can either be static or moving through a roller sheave and may experience tension in the region of 5-20 kN. At the points where the umbilical makes contact with the sheaves or rollers the alternating and/or constant operating tensile loads within the umbilical are supported and absorbed. The contact loads between the rollers and the umbilical act on a small area of the umbilical and the rollers which results in high and varying contact pressures and deformation and ovalisation of the umbilical as the umbilical attempts to resist these loads. It will be understood that as the umbilical passes through the multiple roller sheaves it makes repeated intermittent contact with the rollers which results in differing deformation at any given location along an umbilical.
It has been found that the repeated/cyclic deformation of the umbilical outer jacket translates and passes into the individual hoses within the umbilical core.
Typically the hoses are high pressure thermoplastic hoses which have hose reinforcement layers. The contact forces and aforementioned ovalisation damage the hose pressure containment reinforcement layers due to lateral cyclic compression forces and fibre abrasion between adjacent fibres and the polymers of the pipe core tube and/or the outer jacket occurs due to the relative movement whilst under tensile and lateral compressive loads. This ovalisation and associated damage can result in the hose pressure containment capacity reducing significantly from up to four times that of the working pressure of the hose to levels around actual working pressure such that hose failure may occur in the field during operation when significant operational umbilical life has been consumed. It has been found that this ovalisation and gradual degradation is not linear but exponentially more aggressive at the start of the operational life of an umbilical.
Conventional hoses used in umbilicals generally comprise a hose liner core tube, typically of Nylon 11 or polyethylene which is surrounded by an inner braided layer and an outer braided layer, around which a hose outer jacket is extruded, typically nylon or polyethylene. The braided layers (inner and outer), which provide the appropriate pressure containment, burst and compression resistance are made from braided layers of high strength fibre, typically aramid fibres. Aramid fibres are used extensively in underwater applications, such as umbilicals and hoses, as they provide the required mechanical properties including good axial stiffness and tensile strength. Aramids however have generally poor self abrasion resistance (fibre to fibre) as well as poor abrasion resistance to hose liner core tube materials.
It is an object of the present invention to provide an improved hose for use within an umbilical which avoids or minimises one or more of the aforementioned disadvantages of known systems.